We have continued to study the hydrolytic enzymes of organelles of the myocardium in normal and ischemic conditions. We have quantified the alterations of lysosomal enzymes in well-defined ischemia and have assessed the effects of methylprednisolone and propranolol in a two hour model of canine ischemia. Lysosomal latency has been studied under the above conditions. In addition, we have described in great detail the physical and biochemical conditions required for maintenance of high degree of lysosomal latency in Triton-filled lysosomes. We have continued to develop techniques for examining sarcolemmal structural lipids and membrane-associated enzymes. Work to date has shown active lipases and phospholipases that are associated with the sarcolemma; these enzymes are capable of producing free fatty acids and lysophospholipids in significant quantities. We have studied the attack of the sarcolemma by exogenous phospholipase A2 purified from white cells. The effect of drugs on lipolytic enzymes of the sarcolemma has been reported as well. We are extending these studies to isolated myocytes of the rat and dog. We have isolated beating cardiac muscle cells in high yield and have been using centrifugal gradients to "clean up" these myocytes prior to preparation of organelles such as microsomes, lysosomes and sarcolemma. These studies should provide more accurate quantification of structural conditions on these preparations will be pursued in greater detail.